Hi,
We plan to move our DWH , 5 tera database 11gr2 running on linux machine to exadata 1/4 rac machine.
We are currently running with 32K block size.
Must of our statments are using FTS , and number of indexes is small.
We are to get your advice if we should stick with the 32K block size on the exadata machine , or install the databases on exadata machine with 8K block size.

I guess you need to think how you are going to do the migration. That will determine if you have the option to change the block size. If you go for the simlest ones like transportable tablespace or database you probably can't change the block size. If you do a logical migration you certainly can.

It is likely that this will not have much effect as the storage index sizes are 1mb, asm strip is around 4 mb and recommended minimum extent sizes are 8mb anyway.
thanks